Adjunctive antithrombotic treatment with dual antiplatelet therapy (aspirin + P2Y12 antagonist) plus anticoagulant (heparin or bivalirudin) is a guideline mandated for percutaneous coronary intervention (PCI) patients. Despite aggressive antithrombotic therapy, however, myocardial perfusion after PCI remains inadequate in many patients. Reocclusion from recurrent thrombosis continues to occur, and dose-limiting bleeding occurs in a significant minority of patients. Attempts to further improve clinical outcomes have led to the development of more potent platelet P2Y12 inhibitors including prasugrel and ticagrelor, and direct factor Xa inhibitors, rivaroxaban and apixaban (not approved for PCI), but also increase bleeding complications. Moreover, none of the current antithrombotics provide effective protection against reperfusion injury, defined as myocardial damage caused by the restoration of coronary blood flow after occlusion. Reperfusion injury accounts for up to 50% of the final size of a myocardial infarct, a major determinant for subsequent mortality and morbidity. In patients undergoing PCI, the composite endpoint of adverse cardiovascular events at 30 days after reperfusion remains as high as 7-12%. Meanwhile, 11-12% patients suffer major bleeding. The vast majority of these adverse events occur within the first 6 hours post-intervention. Clearly, beyond optimizing reperfusion therapy, the next milestone is to break the link between antithrombotic potency and bleeding risk and protect the myocardium against microvascular obstruction and necrosis that causes adverse left ventricle remodeling and heart failure in 25% of treated patients. APT402 is a novel therapeutic fusion protein comprised of both antiplatelet and anticoagulant activities. We hypothesize that fusion will target the antithrombotic effect to the site of coronary thrombosis and additively/synergistically attenuate thrombosis and reperfusion injury with minimal bleeding risk. In the carotid electrical vascular injury model in rabbits, we observed APT402 preferably bound to injured site and thrombus. Treatment with clopidogrel, low molecular weight heparin (LMWH, enoxaparin), or bivalirudin (Angiomax, direct and reversible thrombin inhibitor, considered the safest FDA approved anticoagulant) alone failed to fully prevent occlusion with significantly increased bleeding. In contrast, APT402 maintained 100% patency without increasing bleeding time, PT, aPTT, or insertion site hemorrhage. In this fast-track SBIR application, we will determine whether hyperacute treatment with APT402 is more effective to attenuate thrombosis and protect hearts in a highly clinically relevant porcine model of PCI without increasing bleeding compared to the standard-of-care treatment with a P2Y12 antagonist plus anticoagulant. Specific Aim 1. Produce APT402 to support the proposed animal studies (Phase I) and establish a GLP CHO cell line for future cGMP manufacturing (Phase II). Specific Aim 2 (Phase I). To determine minimal effective dose and maximal tolerable dose in the electrical injury model of arterial thrombosis in rabbits. Specific Aim 3 (Phase II). To determine in a porcine model of coronary thrombosis and PCI whether APT402 is more effective and safe to prevent recurrent arterial thrombosis and decrease reperfusion injury within 7 days than P2Y12 antagonist plus anticoagulant infusion.